Electric discharge device



J ly 1952 A. H. REEVES 2,603,765

ELECTRIC DISCHARGE DEVICE Filed May 11, 1948 2 Sl'EETS-SHEET 1 FIG.

Inbentor 141.56 Hflflf) REfVfS A Home y y 15, 1952 A. H. REEVES 2,603,765

ELECTRIC DISCHARGE DEVICE' Filed May i1, 1948 2 SI-lEE'IfS-Sl-IEET 2 F/G. Z4.

/// IF O/IZ INVENTOR. ALEC' H REEVES ATTORN E Y after the other;

Patented July 15, 1952 ELEGTRIG DISCHARGE DEVICE Alec Harley Reeves, London, England, assignor to International'Standard Electric Corporation, New York, N.. Y., a corporation of Delaware Application May 11, 1948, Serial No. 26,281

' In Great Britain May 28, 1947 The present invention relates" to cold cathode electric discharge tubes of the type in which spread of ionisation from .a'discharging gap is arranged to lower the striking potential for a discharge at. a neighbouring gap.

Discharge tubes utilising this principle are described for example. in application No. 763,655, filedjJuly 25, 1947, and-application No. 14,184; fi-led'MarchlB, 1948.. In'general, in tubes of this type; anumber of gaps are-arrangedso that aqsequence of applied'pulses fires first; one, then a second: gap: and then: the remainder ofthe apsof-an: array. Alternatively, when a first pulse :has. been; applied, the general ionisation level may be arranged to besuch that the remaining: aps fire in: sequence, automatically; due to: the finite. time? taken by ionisation. to trayeltfrompne; gap tothe. other, so thatthe striking; potentials for the array of gaps'are loweredtothe voltage of an applied battery one Insuch devices. the total discharge currentdrawn from the battery increases during-- the discharge sequenceand inthe application of the tube. certain difficulties; may be encountered due to the need for a-ve-ry carefully regulated voltage supply system.

Apart from. the question of voltage regula.- tion, there may well beother reasons whyit is desirable that, a discharge from a certain gap should be extinguished after a certain time, rather thanthat a whole .arrayof discharging gaps should Ice-extinguished together. Itisfnot necessary however, that an array or discharge gaps be involved; rather in certain types ofdischarge tubes it may be desired to extinguish just one particular gap which may be the only gap in the tube.

The present invention therefore is particularly concerned with the'problem of extinguishing a discharge from a discharge gap independently of the quenchingof, other discharges that may be present, and, although similar to, is distinguished from, the. invention of application No. 19,083, filed April 5, 1948, now Patent 2,517,599, which is concerned with extinguishing means for an array of gaps.

According to the present invention a cold cathode electric. discharge device comprises, in a gaseous atmosphere a pair of discharge gaps arranged so that ionisation from a. discharge at the first gap or the pair which has. the. lower striking potential shall lower the firing potential of the other, said gaps being arranged with cathodes having different efiective discharge areas, so. that the discharge at the second of-said- 20. Claims. (Cl. 315-201) gaps may pass .a larger discharge current than. the first for the same. applied voltage thereby to extinguish: discharges at both gaps due.,tothe.

actionof' a resistance-capacity network; common to both gap circuits."

As .applied'to sequence discharge tubes'com prising an array of sequentially fired discharge gaps such as are proposed in applicationsNos. 763,655 and:14,184, the present invention provides. a cold cathode dischargedevice comprising,

in agaseous atmosphere; an ordered array-"oi discharge. gapsiarranged so ,that ionisation from a discharge. at one gap shall lower thefiringgaps associated withthe two last mentioned cathodes.

Before proceeding with thedescription' of embodimentsof the invention, it may be as well to recapitulate those principal discharge phenomena 1 which are utilised in devices according tothe' ably below atmospheric pressure. If, now," a'

small voltage be applied to the electrodes a very small current will pass. On increasing the voltage the current will remain at first of very small.

magnitude (say of the order of-microamps) until a critical potential is reached, which potential depends upon the gap separations and the nature and pressure of-the gas. These, though notttheionly criteria, are the main ones which determine that critical voltage which we call the striking or firing. voltage which is sufiicient; to

initiate a discharge in the ,gap between the elec:

trodes;

' Whenonce thedischarge has been started the external. applied voltage. may. bereduced very considerably to a lowerlimiting value. called the maintaining voltage. This potential is a function. principally of the nature and. pressure of the gas. According. to the discharge, current which is permitted. to'pass,.. and hencethenurn.

ber of ions formed. in the gas, the. cathode wil'l.

' electrodes.

. minal I2.

3 be more, or less, covered with a glow which tends to be most pronounced on any protuberances or other surface irregularities. In the case of a cathode surface without pronounced irregularities, so long as the complete surface is not cov ered by the cathode glow, the inter-electrode potential tends to remain constant. This phenomenon is used in familiar voltage stabilisers such as neon tubes and the like. After the whole cathode is covered with glow, the inter-electrode potential will rise with the applied voltage and, in general, in the devices with which we are concerned, discharge currents are maintained in this region. If the externally applied voltage be I reduced below the maintaining voltage, discharge will cease and the gas will become de-ionised at a finite rate in general slower than that required to set up the initial ionisation.

The striking jotential for a discharge gap is very considerably affected by ionisation. It is well known that such ionisation may be caused by radiation of the tube, with ultra-violet light, cosmic'rays, and so on. 1 Of far greater importance however for the present invention, is the ionisation due to previous discharges, or due to discharges already present at another gap in the tube. In a tube with more than one gap, if a discharge has been fired at the first gap, ionisation will spread from this gap to lower the striking potential of the other and at a definite rate which depends, interalia, upon the magnitude of the discharge current passed at the first gap and upon the nature and pressure of the gas.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. l is a schematic diagram of a deviceaccording to the present invention connected in a simple circuit to illustrate its behaviour.

Fig. 2 is a diagrammatic illustration of part of the device of Fig.1.

Fig. 2A is a schematic diagram of a modified form of the device shown in Figs. 1 and '2.

Fig. 3 is a schematic representation of a device and circuit employing discharge gaps according to the present invention, and

Fig. 4 shows a variant of the design of Fig. 3.

To facilitate an understanding of the drawing.

anode plate and a fiat plate 5 substantially paral-' lel with the anode plate. The arrangement of cathode 3 and the anode plate is shown from a different angle in Fig. 2. The striking potential for the gap associated with rod 4 is less than that associated with plate 5.

The tube also comprises a pair of electrodes 6 forming an auxiliary discharge gap in line with electrodes 4 and 5 and closer to 4. Electrodes 4 and 5 are connected together by means of a wire I which is bent away from the anode plate and is preferably coated with alumina or some similar insulating material to inhibit spread of cathodef glow along the wire between the two Wire I is connected through a resistance capacity circuit 8 to the negative pole of battery 9. Anode plate 2 is connected through resistance I0 to the positive pole of this battery, and also through blocking condenser II to ter- The resistance capacity circuit 8 is shunted by'the primary winding of a pulse transformer I 3 in series with a rectifier I 4 and biassing battery I5. A battery I6 is connected in series with a variable resistance I1 across the auxiliary gap electrodes 6. The purpose of the auxiliary discharge electrodes 6 together with their battery circuit is to regulate the general level of ionisation in device I as described, for example, in my U. S. Patent No. 2,520,171, issued August 29, 1950. The voltage of the battery 9, and also? the discharge current passed by the priming gap formed by electrodes 6, is adjusted so that the anodecathode potential of the gaps I8 and I9 formed between the anode plate 2 and respective electrodes 4 and 5 is insufiicient to initiate a discharge at either, but a discharge established at gap I8 is maintained by battery 9. Thus, if a pulse be applied to terminal I2 suflicient to cause gap I8 to strike,'but not gap I 9, then I8 continues discharging. After a certain time depending upon the general ionisation level in the tube, and the separation between gaps I8 and I9, ions from gap I 8 will have reduced the striking potential for gap I9 to that of the applied anode cathode voltage. When this occurs gap I9 will fire. Due to the considerably larger efiective area of plate .5 as compared with red 4, the discharge current at gap I9 will tend to be very much larger than that at I8. In consequence, the potential drop across resistance 20 of the R. C. network 8 will charge up condenser 2I to a value greater than the difference between the potential of battery 9 and the maintaining voltage for the tube- III; the discharges at both gaps I 8 and I9 will be extinguished. The sudden large increase of voltage across network 8 may be utilised by applying the same to the primary of transformer I3; due to the rectifier-battery combination, I4 I5, transformer I3 respondsonly to the sudden large impulses which occurs when gap I 9 fires. A short pulse is thus available at this moment at" the secondary terminals of I3. be applied to terminal I2, then, as pointed out in connection with a very similar circuit in my said U. S. Patent No. 2,520,171, the circuit provides, effectively, a pulse delay network whose' time constant may be varied by changing the bias applied to the primary discharge at auxiliary electrode 6. In an alternative mode of operation for which the priming discharge electrode is not necessary, it may be arranged that gap I9'shall fire on application of a second pulse applied to terminal I2. This demands that either the general ionisation level should be lower than previously, or the pulse should be applied at closer time intervals.

It will be evident that various modifications- .may be made to the device of Fig. 1 without departing from the scope of the present invention.

It is not necessary that an anode plate 2 should be common to both the cathode electrodes 13 and If desired they may be fitted with separate anodes 2 and 2' as shown in Fig. 2A. Similarly, leads to these two electrodes could be taken out of the tube separately, and with such an arrangement it might be more convenient to place a resistance capacity circuit 8 inc. common an ode circuit rather than a common cathode cir-:

which device 22 comprises a flat anode plate 23' and a plurality of cathode pairs 3. Auxiliary cathode 24 forms with the anode plate 23 a priming discharge gap similar to that formed by the electrodes 6 of Fig. 1 and is connected via vari-" able resistance I! to the negative pole of battery I6. The cathode pairs 3 are connected individ- If a train of pulses ace-3 705 ually-ito resistance .capacity:circuits :8 iouts'iderthe' tube envelope'. and. thence to .zthe. negative pole of battery 9. The positive:polenoii'battery it is commonedito the negative pole ofzbattery 9: In place .of thertransformer |.3 .andassociated cir-' cuit of Fig. l; terminals .25-areshow'n.. For simplicity in the. drawings only the." first two pairs and the 'last pair of. cathode pairs 3' are shown,

the remainder being similarly connected. In other respects the circuit arrangements and also the principle of operation'of the device'22; are.

similar-to that described above in connection with: Fig. 1 for one or other .of the Jmodestof operation of device I. Thus inoneimode' of op.-

eration,the general ionisation level," batteryvolt age S and the amplitudel of pulses applied-toterthe only gap'w-hich is fired is the'gap' between the cathode rod of the left hand pairszofcath ode 3. With the disposition of the priming cathode24 as shown, the gap l8'forthis cathode pair will bemore ionised than the remaining...gaps and-consequently willbe the first to fire. It may be arranged that the second pulse of a-pulsetrain fires cathode plate 5 of 'the first cathode pair simultaneously withrod 4 of the second cathode pair 3. For. brevity we may refer to the gap lfl as asmall gap and the gap l9 as a large gap,

Thus, on the secondpulse, thelarge gap of the first cathode pair fires simultaneously with the small gap of the second pair; both dischargesof the first pair are thus extinguishedwhile the second-small gap remains discharging until-the arrival-of the-third pulse,--when discharge at the second pair is in turn extinguished by 'thesecnd large gap being fired at the same time, simultaneously the small gap of the third cathode starts to discharge. Inthis manner, the cathode pairs willfire consecutively throughoutthe array and-"the pulses" corresponding to the discharges at either of the electrodes of each pair may be utilised by beingtaken to'further circuits by the appropriatetermina'li5; g

It should be pointed out thatfor ithef'inanner of operation just described the time constants of the resistance capacity circuits 8 should be considerably larger than the total time occupiedby one pulse train in order to prevent the left ,hand cathode pair 3"flOIIIfiIiDg before the last pair has'been fired.

'As 'analternative mode'ofoperation, ,inijthe same way as'fldescribed'in connection with Fig. 1, itpma-y be" arranged'th'at each large gapjfires automatically ata'definite time "intervalafter a discharge .has been'established at the smalli gap ofthe corresponding pair. Thistime interval may be modified if desired by application of;appropriate' voltages to terminals '25, and in this aspect a device according to the present invention may be used, for example, as a channel demodulator in a multi-channel pulse-modulation system.

A suitable tube for such operation has a gas filling containing 92% neon, 1% argon, 7% hydrogen at a total pressure of 100 millimeters of mercury. The electrodes may be of pure nickel while the spacings may be as follows:

M. m. Distance between cathode pairs 2 Distance between cathode rods and anodes 2 Length of cathode rod 1 A;

The area of the cathode plate is not important so long as it is large and should be arranged to give, say, a peak squeg impulse of to 10 times the current passed by the cathode rod.

.As in the case ofwthe. devicezof ,Fig. ,l',=;alternative arrangements for the device :22 .possible;

for example, the cathode 4. and acould be joined togetherriexternallyz .ofiithe. ztu'be; iif' idesired; an

separate anodes lCOI-lld :beprovided.

A'sfurther. .alternative which may find isome application" where-it is desired'to ileave a cathode discharging rather "longer than .one pulserinter val,'sis showniinzFig. 4,:iniwhich device 26' comprises: an anode=plate 2 as before, and a plurality of cathode "pairs 28 a'rranged-in an ordered array. Pairs 28xidifier fromipa-irs '3 of the previouseX- amples in that the cathode rod of one.z.pair,'-in stea'dlof being j oined .to its neighbouring'plate, is

joined 'to the cathode: platexofithe" next cathode pair in the array. Consequently; .an isolated-rod has' been shown onthe left connected to the plate otthe firstpair'w hile at the other end of :thearray an isolatedplate has' been shownconne'cted .to'the rod of 'th'e 'last pair. In :this device .the left hand rodaiter firing-is not extinguished until the plate of the first cathode pair has-fired, the corresponding rod 'being fired-intermittently. This delay maycorrespondto two ipulse intervalss Similarly, throughout the array, the rod of each: pair re mains discharging for two pulse periods. 'As-the isolated plate at the end of the array doesnot receive ionisation from and partner, it may be placed closer to'the last pair of the array. Insimilar manner, the rod at the front of=the array may be spaced closer to thefirst pair 2-8 than the inter-pair separations.

What- 1s claimed is:

- 'l..'A discharge device comprising a gas-filled envelope enclosingan anode and a pair of directly interconnected cathodes spaced theriefrom, one-of I ther comprising an ionizing electrode-mounted adiacentyone of said cathodes.

4. .A discharge device icomprising a gas-filled envelope enclosingan anode havingafiat surface and apairor. cathodes, one .of-.sa,id cathodes having the shape .oi-arod mounted'with .One

of its endportionsadjacent said 'surfaoerand theother of. said cathodes having. the shape of. a

plate havin ;a surface lar r in area than said. on end por ion and m ans m untin said plate withits-said surface adjacent thefiat surface-of said anode.

5. A discharge device according to claim 4 further comprising an ionizing electrode mounted adjacent said rod-shaped cathode.

6. A discharge device comprising a gas-filled envelope enclosing an anode and a plurality of pairs of cathodes spaced therefrom and mounted adjacent thereto, each pair of cathodes comprising a first cathode having a discharge surface facing said anode and a second cathode having a discharge surface facing said anode greater than the surface of said first cathode.

7. A discharge device according to claim 6 wherein the cathodes of each pair are mounted adjacent each other and each pair is mounted in spaced relation with respect to the other pairs.

8. A discharge device according to claim 7 further comprising means connecting the first cathode of each pair to the second cathode of the next'adjacent pair.

9. A discharge device according to claim 8 further comprising a first further cathode having a discharge surface substantially equal to the discharge surface of said first cathode and mounted in spaced relation to but adjacent one of said pairs 'of cathodes and a second further cathode having a discharge surface substantially equal toithe discharge surface'of said second cathode mounted in spaced relation to but adjacent one of said pairs and mounted remote from said first further cathode.

- 10. A discharge device according to claim 6 furtrier-comprising means connecting the cathodes of each pair together,

11'. A discharge device comprising a gas-filled envelope, enclosing an anode and a pair of cathodes spaced therefrom, one of said cathodes having a discharge surface facing said anode which is larger than the discharge surface of the other cathode facing said anode, means connecting said cathodes together, a source of potential, and means connecting the positive end of said source to said anode and the negative end to said cathodes, said last-mentioned-means including a load impedance.

12. A discharge device accordingto claim 11 wherein said load impedance comprises a resistor and a condenser connected in parallel with each other and in series with said source.

13. A discharge device according to claim 12 further comprising an output impedance, 9, rectifier and a further source of potential andmeans connecting said output impedance, said rectifier and said further source in series and in parallel with said load impedance.

14. A discharge device according to claim 11 further comprising means for producing ions mounted adjacent one of said cathodes.

l5..A discharge device according to claim 11 further comprising a pulse source and means coupling said source to said anode 16. A discharge device comprising a gas-filled envelope enclosing an anode and a plurality of pairs of cathodes spaced therefrom and mounted adjacent thereto, each pair of cathodes comprising a first cathode having a discharge surface facing said anode and a second cathode having adischarge surface facing said anode greater than the surface of said first cathode, means connecting pairs of said cathodes together, a source of potential, and means connecting the positive end of said source to said anode and the negative end to said connected pairs ofcathodes, said lastmentioned means including a load impedance;

-17. A discharge device comprising a gas-filled envelope enclosing an anodeand a plurality of pairs of cathodes spaced therefrom and mounted adjacent thereto, each'pair of cathodes comprising a first cathode having a discharge surface facing said anode and'a second cathode having a discharge surface facing said anode greater than the surface of said first cathode, means connecting the cathodes of each 'pair together, a source of potential, and means connecting the positive end of said sourceto said anode and the negative end to said connected cathodes, said last-mentioned means including a plurality of load impedances each comprising a resistor and a condenser connected in parallel and each connected between said source and one of said connected pairs of cathodes.

18. A discharge device according further comprising an ionizing electrode mounted adjacent said anode and one of said pairs of cathodes and a source of potential connected to said electrode.

19. A discharge'device comprising a gas-filled envelope enclosing an anode and a plurality of pairs of cathodes spaced therefrom and mounted adjacent thereto, each pair of cathodes comprising afirst cathode having a discharged surface facing said anode and a second anode having a discharge'surface facing said anode greater than the surface of said first cathode, means connecting the first cathode of each pair to the second cathode of the next adjacent pair, a source of potential and means connecting the positive end of said source to said anode and the negative end to said connected cathodes, said lastmentioned means including load impedances connected between each connected pair of cathodes and said source.

20. A discharge device according to claim 19 wherein said load impedances each comprises a resistor and a condenser connected in parallel. v

ALEC HARLEY REEVES.

REFERENCES CITED The following references are of record in the file ofthis patent:

Wales, Jr June '15, 1948 to claim 17 

